Doping of zinc oxide particles for sunscreen applications

ABSTRACT

Zinc oxide compositions as well as techniques for doping ZnO particles for sunscreen applications are provided herein. A method includes selecting one or more dopants to be incorporated into one or more zinc oxide particles in a sunscreen composition, wherein the one or more dopants comprise chromium, cobalt, gallium, and/or tin, and wherein said selecting is based on one or more optical properties associated with each of the dopants, and incorporating the selected dopants into the zinc oxide particles to create the sunscreen composition. A composition includes multiple zinc oxide particles suspended within a medium forming sunscreen composition, and one or more dopants incorporated into each of the multiple zinc oxide particles, wherein the one or more dopants comprise chromium, cobalt, gallium, and/or tin, and wherein each of the dopants imparts one or more optical properties to the zinc oxide particle within which the dopant is incorporated.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Provisional ApplicationSer. No. 62/213,658, filed Sep. 3, 2015, incorporated by referenceherein.

FIELD

The present application generally relates to chemical technology, and,more particularly, to sunscreen technologies.

BACKGROUND

Sunscreen creams and other such compositions are commonly used toprevent ultraviolet (UV) radiation (also referred to herein as “light”in this context) from reaching the skin of a human user and causingdamage. It is noted that UV light is an electromagnetic radiation with awavelength range between approximately 280 nanometers (nm) andapproximately 400 nanometers (specifically, that is the range of UVradiation that is not absorbed by the ozone).

A common active ingredient of existing sunscreen compositions is zincoxide (ZnO). ZnO is a semiconductor that has a specific band gap, andparticles of ZnO used in existing sunscreen compositions are typicallyapproximately 50-200 nm in size. Additionally, in existing sunscreencompositions, typical ZnO materials are capable of absorbing UV light(that is, blocking the UV light from passing through the sunscreencomposition to be absorbed by the skin of the user) within a wavelengthrange of approximately 290 nm through only approximately 350-380 nm.

Additionally, high sun protection factor (SPF) sunscreen compositions,which can absorb a large majority of the UV light in the range of290-380 nm, require the addition of a higher density of ZnO particles,which causes the composition to become white and/or opaque due to lightscattering from the ZnO particles, and which is an often undesirableproperty to consumers.

SUMMARY

In one embodiment of the present invention, zinc oxide compositions,methods of fabrications thereof and methods of use thereof are provided.An exemplary method can include steps of selecting one or more dopantsto be incorporated into one or more zinc oxide particles in a sunscreencomposition, wherein the one or more dopants comprise at least one ofchromium, cobalt, gallium, and tin, and wherein said selecting is basedon one or more optical properties associated with each of the dopants.The method also includes incorporating the one or more selected dopantsinto the one or more zinc oxide particles to create the sunscreencomposition.

In another embodiment of the invention, a composition can includemultiple zinc oxide particles suspended within a medium formingsunscreen composition, and one or more dopants incorporated into each ofthe multiple zinc oxide particles, wherein the one or more dopantscomprise at least one of chromium, cobalt, gallium, and tin, and whereineach of the dopants imparts one or more optical properties to the zincoxide particle within which the dopant is incorporated.

These and other objects, features and advantages of the presentinvention will become apparent from the following detailed descriptionof illustrative embodiments thereof, which is to be read in connectionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating doped ZnO particles, according to anexemplary embodiment of the invention; and

FIG. 2 is a flow diagram illustrating techniques, according to anembodiment of the invention.

DETAIL ED DESCRIPTION

As described herein, an embodiment of the present invention includes ZnOcompositions as well as techniques for doping ZnO particles forsunscreen applications. As further detailed herein, one or moreembodiments of the invention include generating ZnO compositions andmethods of use thereof for effectively blocking more and/or all of thecomplete spectrum of UV light (that is, as noted above, the UV radiationthat is not absorbed by the ozone, and which ranges betweenapproximately 280 nm and 400 nm) while also preventing whitening effectscaused by the scattering of light in the visible spectrum (that is,radiation between approximately 400 nm and 700 nm). As used herein,“scattering” refers to the deflection of rays of visible light from therays' original path due to interaction with particle surfaces.

As further detailed herein, one or more embodiments of the inventioninclude generating ZnO compositions and methods of use thereof foreffectively modifying the band gap of a ZnO composition via theincorporation of one or more additional materials into the composition.For example, at least one embodiment of the invention can includemodifying the absorption onset of a ZnO composition from approximately375 nm to approximately 410 nm.

At least one embodiment of the invention includes doping ZnO particleswith one or more transition metals to increase absorption by the ZnOparticles in sunscreen applications. By way of example, in one or moreembodiments of the invention, the addition of one or more dopants to ZnOparticles can result in 400 nm absorption. Such addition can encompassup to approximately 10% (atomic percent) of dopant. Example dopants, inaccordance with one or more embodiments of the invention, can includechromium (Cr), copper (Cu), cobalt (Co), gallium (Ga), aluminum (Al),and/or tin (Sn).

In at least one embodiment of the invention, addition of one or moredopants to ZnO particles can decrease the band gap of the ZnO particles.

As used herein, and as is to be appreciated by one skilled in the art, aband gap represents the minimum amount of energy required to causeelectrons to transition from the collection of electronic ground states(that is, the valence band) to an available unfilled excited electronicstate (that is, the conduction band). By way merely of illustration, ina perfect semiconductor, there are no available electronic states inbetween the valence band and the conduction band. However, in imperfectmaterials, various defects can introduce electronic states into thisotherwise forbidden energy gap. For example, in at least one embodimentof the invention, addition of one or more dopants to ZnO particles canimprove the absorption properties of the ZnO particles in a spectralregion of interest (for instance, 280-410 nm).

There are multiple mechanisms by which dopants can increase absorptionin ZnO in the spectral range of 280-410 nm. Such mechanisms can include,for example: (i) the introduction of electronic states (associated withthe dopants) inside of the band gap of ZnO, where these states may beoptically active (that is, electrons can be promoted to or from thesestates into and/or out of the conduction and valence bands); (ii)dopants can cause lattice strain due to a difference in size between thehost atoms and the impurity atoms (dopants), and this strain canincrease or decrease the band gap of ZnO depending on whether the strainis compressive or tensile; and (iii) the presence of dopants and/ordefects can induce band tailing in the ZnO due to local electronic orstructural fluctuations, which can increase sub-band gap absorption.

Additionally, in one or more embodiments of the invention, addition ofone or more dopants to ZnO particles can introduce one or moreadditional states inside of the band gap of the ZnO particles, whichallow and/or facilitate the ZnO particles to absorb lower-energy light.Due to differences in local bonding between the impurity atom (dopant)and the host crystal (ZnO, for example), new electronic states can beintroduced inside of the band gap (of the host crystal). Additionally,if there is more than one configuration for the dopant to incorporateinto the structure, the same dopant can introduce multiple states. Forexample, if an impurity atom can occupy either a Zn site or aninterstitial site, then it is possible for that impurity atom tointroduce more than one type of electronic state into the band gap ofZnO.

FIG. 1 is a diagram illustrating doped ZnO particles, according to anembodiment of the invention. By way of illustration, FIG. 1 depictsmultiple ZnO particles doped with various dopants within a sunscreencomposition. Specifically, FIG. 1 depicts a Ga-doped ZnO particle 102, aCo-doped ZnO particle 104, a Cu-doped ZnO particle 106, a Sn-doped ZnOparticle 108, and a Cr-doped ZnO particle 110. Accordingly, asillustrated in FIG. 1, a collection of multiple ZnO particles within asunscreen composition can be doped by multiple distinct dopants.Alternatively, in one or more embodiments of the invention, a collectionof multiple ZnO particles within a sunscreen composition can be doped bya single type of dopant. Further, multiple dopants can be used inconnection with a single ZnO particle.

FIG. 2 is a flow diagram illustrating techniques, according to anembodiment of the present invention. Step 202 includes selecting one ormore dopants to be incorporated into one or more zinc oxide particles ina sunscreen composition, wherein the one or more dopants comprise atleast one of chromium, cobalt, gallium, and tin, and wherein saidselecting is based on one or more optical properties associated witheach of the dopants.

The optical properties can include, for example, increasing the lightabsorption capabilities of the one or more zinc oxide particles. In suchan embodiment of the invention, the increased absorption of light caninclude 400 nanometer absorption capabilities. Additionally, the opticalproperties can include decreasing the band gap of the zinc oxideparticles, providing a color center within the zinc oxide particles,and/or introducing one or more additional states inside the band gap ofthe zinc oxide particles.

In one or more embodiments of the invention, the one or more dopants caninclude two or more dopants to be incorporated into the one or more zincoxide particles. Additionally, in one or more embodiments of theinvention, the one or more dopants can include a combination of two ormore dopants to be incorporated into each of the one or more zinc oxideparticles. Further, in at least one embodiment of the invention, the oneor more dopants can include a single dopant to be incorporated into theone or more zinc oxide particles.

Step 204 includes incorporating the one or more selected dopants intothe one or more zinc oxide particles to create the sunscreencomposition. Incorporating can include incorporating up to approximatelyten atomic percent, of the sunscreen composition, of the one or moreselected dopants into the one or more zinc oxide particles.

Also, an additional embodiment of the invention includes a compositionthat includes multiple zinc oxide particles suspended within a mediumforming sunscreen composition, and one or more dopants incorporated intoeach of the multiple zinc oxide particles, wherein the one or moredopants comprise at least one of chromium, cobalt, gallium, and tin, andwherein each of the dopants imparts one or more optical properties tothe zinc oxide particle within which the dopant is incorporated. In sucha composition, the one or more dopants incorporated into each of themultiple zinc oxide particles can include up to approximately ten atomicpercent, of the sunscreen composition, of the one or more dopants.

Also, in such a composition, the optical properties can include at leastone of: (i) increasing the light absorption capabilities of the zincoxide particle within which the dopant is incorporated, (ii) decreasingthe band gap of the zinc oxide particle within which the dopant isincorporated, (iii) providing a color center within the zinc oxideparticle within which the dopant is incorporated, and (iv) introducingone or more additional states inside the band gap of the zinc oxideparticle within which the dopant is incorporated. Such opticalproperties achieve the objective of increasing ZnO absorption in thespectral region of 280-400 nm.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a,” “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of anotherfeature, step, operation, element, component, and/or group thereof.

At least one embodiment of the present invention may provide abeneficial effect such as, for example, effectively modifying the bandgap of a ZnO composition via the incorporation of one or more dopantsinto the composition.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed is:
 1. A composition comprising: multiple zinc oxide particles suspended within a medium forming a sunscreen composition; and multiple dopants incorporated into the multiple zinc oxide particles, wherein the dopants consist of copper, chromium, cobalt, gallium, aluminum, and tin, and wherein each of the dopants imparts one or more optical properties to the zinc oxide particle within which the dopant is incorporated.
 2. The composition of claim 1, wherein the dopants incorporated into the multiple zinc oxide particles comprise up to approximately ten atomic percent, of the sunscreen composition, of the dopants.
 3. The composition of claim 1, wherein the one or more optical properties comprise increasing the light absorption capabilities of the zinc oxide particle within which the dopant is incorporated.
 4. The composition of claim 3, wherein the increased absorption of light comprises 400 nanometer absorption capabilities.
 5. The composition of claim 1, wherein the one or more optical properties comprise introducing one or more additional states inside the band gap of the zinc oxide particle within which the dopant is incorporated. 